Phosphepine matrix compound for a semiconducting material

ABSTRACT

The present invention is directed to a compound comprising at least one phosphepine ring and having the phosphorous atom of the phosphepine ring substituted with at least one monovalent substituent R, wherein (i) R is selected from aryls and heteroaryls comprising at least two rings or (ii) R is selected from aryls, alkyls, heteroalkyls, heteroaryls, H, F, CI, Br, I, OH, and OR*, wherein R* is selected from C1-C22 alkyl and C7-C22 arylalkyl, and the hosphepine ring is a ring according to formula (I), wherein structural moieties A, B, C are independently selected from ortho-arylenes and ortho-heteroarylenes, with the proviso that neither A nor B is a condensed arylene, and C comprises at least two annelated rings, a semiconducting material comprising this compound as well as an electronic device comprising the semiconducting material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application ofPCT/EP2016/064430, filed Jun. 22, 2016, which claims priority to GermanApplication No. 102015110091.6, filed Jun. 23, 2015. The contents ofthese applications are hereby incorporated by reference.

The present invention concerns new organic compounds comprising aphosphepine ring and their use as and/or in semiconducting materials,semiconducting materials with improved electrical properties thatcomprise the new phosphepine matrix compound and electronic devicesutilizing the new phosphepine compound and/or improved electricalproperties of the inventive semiconducting material.

I. BACKGROUND OF THE INVENTION

Among the electronic devices comprising at least a part based onmaterial provided by organic chemistry, organic light emitting diodes(OLEDs) have a prominent position. Since the demonstration of efficientOLEDs by Tang et al. in 1987 (C. W. Tang et al., Appl. Phys. Lett. 51(12), 913 (1987)), OLEDs developed from promising candidates to high-endcommercial displays. An OLED comprises a sequence of thin layerssubstantially made of organic materials. The layers typically have athickness in the range of 1 nm to 5 μm. The layers are usually formedeither by means of vacuum deposition or from a solution, for example bymeans of spin coating or jet printing.

OLEDs emit light after the injection of charge carriers in the form ofelectrons from the cathode and in form of holes from the anode intoorganic layers arranged in between. The charge carrier injection iseffected on the basis of an applied external voltage, the subsequentformation of excitons in a light emitting zone and the radiativerecombination of those excitons. At least one of the electrodes istransparent or semitransparent, in the majority of cases in the form ofa transparent oxide, such as indium tin oxide (ITO), or a thin metallayer.

Some phosphepine compounds are known in the scientific literature, e.g.formation of11-phenylbenzo[b]dinaphtho-[2,1-d:1′,2″-f]phosphepine-11-oxide (CAS597578-28-6) by an intramolecular substitution reaction was reported inBull. Chem. Soc. Jpn., 76, 1233-1244 (2003).

It is an objective of the invention to overcome the drawbacks of theprior art and to find new compounds which can improve the performance oforganic electronic devices. Specifically, the sought compounds shall besuccessfully embedded in electrically doped semiconducting materials foruse in electronic devices. The inventive semiconducting materials shallafford devices with better characteristics, especially with low voltageand higher efficiency, more specifically, OLEDs with higher powerefficiency, even more specifically, OLEDs having satisfactory efficiencyand long lifetime.

II. SUMMARY OF THE INVENTION

The object is achieved by a compound comprising at least one phosphepinering and having the phosphorus atom of the phosphepine ring substitutedwith at least one monovalent substituent R, wherein

(i) R is selected from aryls and heteroaryls comprising at least tworings, or

(ii) R is selected from aryls, alkyls, heteroalkyls, heteroaryls, H, F,Cl, Br, I, OH, and OR*, wherein R* is selected from C1-C22 alkyl andC7-C22 arylalkyl, and the phosphepine ring is a ring according toformula (I)

wherein structural moieties A, B, C are independently selected fromortho-arylenes and ortho-heteroarylenes, with the proviso that neither Anor B is a condensed arylene, and C comprises at least two annelatedrings. In formula (I), the phosphorous atom shall also bear themonovalent substituent R.

Preferably, the compound comprising at least one phosphepine ringcomprises at least one phosphine oxide group.

More preferably, the phosphepine ring is a phosphepine-P-oxide ring.Also preferably, the substituent R is selected from C₁₀-C₆₆ aryl andC₄-C₆₆ heteroaryl. Most preferably, the compound comprising at least onephosphepine ring is used as a charge transporting matrix.

It is to be understood that the structural moiety C in formula (I) maybe an arylene or a heteroarylene comprising at least two annelated ringsitself, like a naphtylene or an anthrylene, or may contain at least onearyl or heteroaryl substituent comprising at least two annelated rings.The structural moiety C thus may be also e.g. an ortho phenylene or anortho thienylene, provided that it is substituted with at least onegroup comprising annelated rings like napthtyl, indenyl, indolyl,quinolyl, fluorenyl, anthryl, adamantyl, and like.

It is further understood that annelated rings may be comprised also insubstituents attached to structural moieties A and B, and despite it isnot particularly preferable, a ring may be annelated directly to theo-arylene or o-heteroarylene ring of any of the structural moieties Aand B, provided that such directly annelated ring is not aromatic orheteroaromatic.

The object is further achieved by a semiconducting material comprisingat least one matrix compound, wherein the matrix compound comprises atleast one phosphepine ring having the phosphorus atom substituted withat least one monovalent substituent R, and

(i) R is selected from aryls and heteroaryls comprising at least tworings or H, F, Cl, Br, I, OH, and OR*, wherein R* is selected fromC1-C22 alkyl and C7-C22 arylalkyl, or

(ii) the phosphepine ring has the constitution according to formula (I)

wherein structural moieties A, B, C are independently selected fromortho-arylenes and ortho-heteroarylenes, with the proviso that neither Anor B is a condensed arylene and C comprises at least two annelatedrings. Examples of o-arylenes are o-phenylene, 3-methylbenzene-1,2-diyl,4,5-dimethylbenzene-1,2-diyl, 4,5-dimethoxybenzene-1,2-diyl,4,5-methylenedioxy-benzene-1,2-diyl, naphthalene-1,2-diyl,naphthalene-2,3-diyl, anthracene-1,2-diyl, anthracene-2,3-diyl,phenanthrene-5,6-diyl, and like. Examples of o-heteroarylenes arethiophene-2,3-diyl, thiophene-3,4-diyl, furane-2,3-diyl, furan-3,4-diyl,benzo[b]thiophene-2,3-diyl, 1-phenyl-1H-indole-2,3-diyl,pyridine-2,3-diyl, quinoline-2,3-diyl, and like. Optionally, thesemiconducting material further comprises at least one dopant. In one ofpreferred embodiments, the dopant is an electrical dopant. In one ofpreferred embodiments, the compound comprising the phosphepine ringcomprises at least one phosphine oxide group. Also preferably, thephosphepine ring is a phosphepine-P-oxide ring. In another preferredembodiment, the electrical dopant is a n-dopant. Also preferably, thedopant is a metal, a metal salt or a metal complex.

In a further preferred embodiment, the metal complex is a compoundcomprising at least one ligand attached to the metal atom through atleast one oxygen atom and through at least one nitrogen atom, and themetal, oxygen and nitrogen atom are comprised in a 5-, 6- or 7-memberedring. Example of such ligand is 8-hydroxyquinolinolato ligand.

In another preferred embodiment, the metal complex has formula (II)

wherein A¹ is a C₆-C₃₀ arylene or C₂-C₃₀ heteroarylene comprising atleast one atom selected from O, S and N in an aromatic ring and each ofA²-A³ is independently selected from a C₆-C₃₀ aryl and C₂-C₃₀ heteroarylcomprising at least one atom selected from O, S and N in an aromaticring. Preferred example of A¹ is phenylene, preferred examples of A² andA³ are phenyl and pyridyl.

The phosphepine compound has preferably structure according to

-   -   (i) formula (Ia):

-   -   wherein R¹ is selected from aryls and heteroaryls comprising at        least two rings, and R²-R³ is a chain of six carbon atoms        comprising six pi-electrons, optionally substituted with        hydrocarbon groups comprising overall up to 60 carbon atoms or        with substituents consisting of overall up to 100 covalently        bound atoms selected preferably from C, H, B, Si, N, O, S, P, F,        Cl, Br and I, or    -   (ii) formula (Ib)

-   -   wherein R⁴ is selected from C₆-C₆₀ aryl and from C₂-C₆₀        heteroaryl comprising up to 12 heteroatoms selected preferably        from B, N, O, S and the structural moieties A, B, C are defined        as in the formula (I) above.

If not explicitly stated that a group or structural unit isunsubstituted, the given count of atoms (e.g., given count of carbonatoms) comprises also possible substituents. For example, the overallcount of carbon atoms in aryls or heteroaryls comprises also possiblesubstitution with alkyl, cycloalkyl or arylalkyl groups, which may bealso linked to form ring structures annelated to the aromatic orheteroaromatic core of the structural moieties A, B, C, R⁴. Similarly,the phosphepine ring in formula (Ia) is broadly defined as a ringcomprising one phosphorus atom and a chain of six carbon atomscomprising six pi-electrons (which are most conventionally described asthree conjugated double bonds), and the definition of formula (Ia)encompasses any chemically reasonable substitution with hydrogen orhalogen atoms, hydrocarbon groups, substituted hydrocarbon groups, orother substituents comprising heteroatoms, and these substituents maycomprise ring structures and/or form ring structures annelated to thecore phosphepine ring.

Preferably, the semiconducting material comprising the dopant and thephosphepine matrix compound serves as an electron transporting materialor as an electron injecting material, or fulfils both electrontransporting and hole blocking function.

It is preferred that the semiconducting material according to theinvention comprises the dopant and the phosphepine matrix compound atleast partly in form of a homogeneous mixture, wherein both componentsare molecularly dispersed in each other.

Another object the invention is achieved by an electronic devicecomprising, preferably between two electrodes, at least onesemiconducting material comprising the new phosphepine matrix compoundas described above. Preferably, the inventive semiconducting materialcomprising the phosphepine matrix compound forms at least one layerbetween a cathode and an anode.

Specifically, the third object of the invention is represented by anelectronic device comprising at least one semiconducting layercomprising the doped semiconducting material according to the inventionor consisting of it. More specifically, the semiconducting materialaccording to the invention is used in the electronic device as anelectron transporting layer, as an electron injecting layer, or as alayer having double electron transporting and hole blocking function.

Preferred examples of the electronic device comprising thesemiconducting material according to the invention are organic diodesand organic transistors. More preferably, the electronic device is alight emitting device. Most preferably, the light emitting device is anorganic light emitting diode.

III. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic illustration of a device in which the presentinvention can be incorporated.

FIG. 2 shows a schematic illustration of a device in which the presentinvention can be incorporated.

FIG. 3 shows the current density versus applied bias for thesemiconducting material E1+D2 and comparative materials C1+D2, C2+D2,C3+D2 and C4+D2 in example 1.

FIG. 4 shows the current efficiency versus current density for thesemiconducting material E1+D2 and comparative materials C1+D2, C2+D2,C3+D2 and C4+D2 in example 1.

IV. DETAILED DESCRIPTION OF THE INVENTION

Device Architecture

FIG. 1 shows a stack of anode (10), organic semiconducting layer (11)comprising the light emitting layer, electron transporting layer (ETL)(12), and cathode (13). Other layers can be inserted between thosedepicted, as explained herein.

FIG. 2 shows a stack of an anode (20), a hole injecting and transportinglayer (21), a hole transporting layer (22) which can also aggregate thefunction of electron blocking, a light emitting layer (23), an ETL (24),and a cathode (25). Other layers can be inserted between those depicted,as explained herein.

The wording “device” comprises the organic light emitting diode.

Material Properties—Energy Levels

A method to determine the ionization potentials (IP) is the ultravioletphoto spectroscopy (UPS). It is usual to measure the ionizationpotential for solid state materials; however, it is also possible tomeasure the IP in the gas phase. Both values are differentiated by theirsolid state effects, which are, for example the polarization energy ofthe holes that are created during the photo ionization process. Atypical value for the polarization energy is approximately 1 eV, butlarger discrepancies of the values can also occur. The IP is related tobeginning of the photoemission spectra in the region of the largekinetic energy of the photoelectrons, i.e. the energy of the most weaklybounded electrons. A related method to UPS, the inverted photo electronspectroscopy (IPES) can be used to determine the electron affinity (EA).However, this method is less common. Electrochemical measurements insolution are an alternative to the determination of solid stateoxidation (E_(ox)) and reduction (E_(red)) potential. An adequate methodis for example the cyclo-voltammetry. A simple rule is used very oftenfor the conversion of red/ox potentials into electron affinities andionization potential: IP=4.8 eV+e*E_(ox) (vs. ferroceniurn/ferrocene(Fc⁺/Fc)) and EA=4.8 eV+e*E_(red) (vs. Fc⁺/Fc) respectively (see B. W.D'Andrade, Org. Electron. 6, 11-20 (2005)). Processes are known for thecorrection of the electrochemical potentials in the case other referenceelectrodes or other redox pairs are used (see A. J. Bard, L. R. Faulkner“Electrochemical Methods: Fundamentals and Applications”, Wiley, 2.Ausgabe 2000). The information about the influence of the solution usedcan be found in N. G. Connelly et al., Chem. Rev. 96, 877 (1996). It isusual, even if not exactly correct to use the terms “energy of the HOMO”E_((HOMO)) and “energy of the LUMO” E_((LUMO)) respectively as synonymsfor the ionization energy and electron affinity (Koopmans theorem). Ithas to be taken in consideration, that the ionization potentials and theelectron affinities are given in such a way that a larger valuerepresents a stronger binding of a released or respectively of anabsorbed electron. The energy scale of the frontier molecular orbitals(HOMO, LUMO) is opposed to this. Therefore, in a rough approximation, isvalid: IP=−E_((HOMO)) and EA=E_((LUMO)). The given potentials correspondto the solid-state potentials.

Substrate

It can be flexible or rigid, transparent, opaque, reflective, ortranslucent. The substrate should be transparent or translucent if thelight generated by the OLED is to be transmitted through the substrate(bottom emitting). The substrate may be opaque if the light generated bythe OLED is to be emitted in the direction opposite of the substrate,the so called top-emitting type. The OLED can also be transparent. Thesubstrate can be either arranged adjacent to the cathode or anode.

Electrodes

The electrodes are the anode and the cathode, they must provide acertain amount of conductivity, being preferentially conductors.Preferentially the “first electrode” is the cathode. At least one of theelectrodes must be semi-transparent or transparent to enable the lighttransmission to the outside of the device. Typical electrodes are layersor a stack of layer, comprising metal and/or transparent conductiveoxide. Other possible electrodes are made of thin busbars (e.g. a thinmetal grid) wherein the spaces between the busbars is filled (coated)with a transparent material with a certain conductivity, such asgraphene, carbon nanotubes, doped organic semiconductors, etc.

In one mode, the anode is the electrode closest to the substrate, whichis called non-inverted structure. In another mode, the cathode is theelectrode closest to the substrate, which is called inverted structure.

Typical materials for the Anode are ITO and Ag. Typical materials forthe cathode are Mg:Ag (10 vol. % of Mg), Ag, ITO, Al. Mixtures andmultilayer are also possible.

Preferably, the cathode comprises a metal selected from Ag, Al, Mg, Ba,Ca, Yb, In, Zn, Sn, Sm, Bi, Eu, Li, more preferably from Al, Mg, Ca, Baand even more preferably selected from Al or Mg. Preferred is also acathode comprising an alloy of Mg and Ag.

Hole-Transporting Layer (HTL)

Is a layer comprising a large gap semiconductor responsible to transportholes from the anode or holes from a CGL to the light emitting layer(LEL). The HTL is comprised between the anode and the LEL or between thehole generating side of a CGL and the LEL. The HTL can be mixed withanother material, for example a p-dopant, in which case it is said theHTL is p-doped. The HTL can be comprised by several layers, which canhave different compositions. P-doping the HTL lowers its resistivity andavoids the respective power loss due to the otherwise high resistivityof the undoped semiconductor. The doped HTL can also be used as opticalspacer, because it can be made very thick, up to 1000 nm or more withoutsignificant increase in resistivity.

Suitable hole transport materials (HTM) can be, for instance HTM fromthe diamine class, where a conjugated system is provided at leastbetween the two diamine nitrogens. Examples areN4,N4′-di(naphthalen-1-yl)-N4,N4′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(HTM1), N4,N4,N4″,N4″-tetra([1,1′-biphenyl]-4-yl)-[1,1′:4′,1″-terphenyl]-4,4″-diamine(HTM2). The synthesis of diamines is well described in literature; manydiamine HTMs are readily commercially available.

Hole-Injecting Layer (HIL)

Is a layer which facilitates the injection of holes from the anode orfrom the hole generating side of a CGL into an adjacent HTL. Typicallythe HIL is a very thin layer (<10 nm). The hole injection layer can be apure layer of p-dopant and can be about 1 nm thick. When the HTL isdoped, an HIL may not be necessary, since the injection function isalready provided by the HTL.

Light-Emitting Layer (LEL)

The light emitting layer must comprise at least one emission materialand can optionally comprise additional layers. If the LEL comprises amixture of two or more materials the charge carrier injection can occurin different materials for instance in a material which is not theemitter, or the charge carrier injection can also occur directly intothe emitter. Many different energy transfer processes can occur insidethe LEL or adjacent LELs leading to different types of emission. Forinstance excitons can be formed in a host material and then betransferred as singlet or triplet excitons to an emitter material whichcan be singlet or triplet emitter which then emits light. A mixture ofdifferent types of emitter can be provided for higher efficiency. Mixedlight can be realized by using emission from an emitter host and anemitter dopant.

Blocking layers can be used to improve the confinement of chargecarriers in the LEL, these blocking layers are further explained in U.S.Pat. No. 7,074,500 B2.

Electron-Transporting Layer (ETL)

Is a layer comprising a large gap semiconductor responsible to transportelectrons from the cathode or electrons from a CGL or EIL (see below) tothe light emitting layer (LEL). The ETL is comprised between the cathodeand the LEL or between the electron generating side of a CGL and theLEL. The ETL can be mixed with an electrical n-dopant, in which case itis said the ETL is n-doped. The ETL can be comprised by several layers,which can have different compositions. Electrical n-doping the ETLlowers its resistivity and/or improves its ability to inject electronsinto an adjacent layer and avoids the respective power loss due to theotherwise high resistivity (and/or bad injection ability) of the undopedsemiconductor. The doped ETL can also be used as optical spacer, becauseit can be made very thick, up to 1000 nm or more without significantincrease in resistivity.

The present invention may exploit an inventive phosphepine compound,preferably a compound according to formula (Ia) or (Ib) in the ETL. Theinventive phosphepine compound can be used in combination with othermaterials, in the whole layer or in a sub-layer of the ETL.

Hole blocking layers and electron blocking layers can be employed asusual.

Other layers with different functions can be included, and the devicearchitecture can be adapted as known by the skilled in the art. Forexample, an Electron-Injecting Layer (EIL) can be used between thecathode and the ETL. Also the EIL can comprise the inventive matrixcompounds of the present application.

Charge Generation Layer (CGL)

The OLED can comprise a CGL which can be used in conjunction with anelectrode as inversion contact, or as connecting unit in stacked OLEDs.A CGL can have the most different configurations and names, examples arepn-junction, connecting unit, tunnel junction, etc. Best examples are pnjunctions as disclosed in US 2009/0045728 A1, US 2010/0288362 A1. Metallayers and or insulating layers can also be used.

Stacked OLEDs

When the OLED comprises two or more LELs separated by CGLs, the OLED isnamed a stacked OLED, otherwise it is named a single unit OLED. Thegroup of layers between two closest CGLs or between one of theelectrodes and the closest CGL is named a electroluminescent unit (ELU).Therefore a stacked OLED can be described asanode/ELU₁/{CGL_(X)/ELU_(1+X)}_(X)/cathode, wherein x is a positiveinteger and each CGL_(X) or each ELU_(1+X) can be equal or different.The CGL can also be formed by the adjacent layers of two ELUs asdisclosed in US2009/0009072 A1. Further stacked OLEDs are explained e.g.in US 2009/0045728 A1, US 2010/0288362 A1, and references therein.

Deposition of Organic Layers

Any organic semiconducting layers of the inventive display can bedeposited by known techniques, such as vacuum thermal evaporation (VTE),organic vapour phase deposition, laser induced thermal transfer, spincoating, blade coating, slot dye coating, inkjet printing, etc. Apreferred method for preparing the OLED according to the invention isvacuum thermal evaporation.

Preferably, the ETL is formed by evaporation. When using an additionalmaterial in the ETL, it is preferred that the ETL is formed byco-evaporation of the electron transporting matrix (ETM) and theadditional material. The additional material may be mixed homogeneouslyin the ETL. In one mode of the invention, the additional material has aconcentration variation in the ETL, wherein the concentration changes inthe direction of the thickness of the stack of layers. It is alsoforeseen that the ETL is structured in sub-layers, wherein some but notall of these sub-layers comprise the additional material.

Electrical Doping

The present invention can be used in addition or in combination withelectrical doping of organic semiconducting layers.

The most reliable and at the same time efficient OLEDs are OLEDscomprising electrically doped layers. Generally, the electrical dopingmeans improving of electrical properties, especially the conductivityand/or injection ability of a doped layer in comparison with neatcharge-transporting matrix without a dopant. In the narrower sense,which is usually called redox doping or charge transfer doping, holetransport layers are doped with a suitable acceptor material (p-doping)or electron transport layers with a donor material (n-doping),respectively. Through redox doping, the density of charge carriers inorganic solids (and therefore the conductivity) can be increasedsubstantially. In other words, the redox doping increases the density ofcharge carriers of a semiconducting matrix in comparison with the chargecarrier density of the undoped matrix. The use of doped charge-carriertransport layers (p-doping of the hole transport layer by admixture ofacceptor-like molecules, n-doping of the electron transport layer byadmixture of donor-like molecules) in organic light-emitting diodes is,e.g., described in US 2008/203406 and U.S. Pat. No. 5,093,698.US2008227979 discloses in detail the charge-transfer doping of organictransport materials, with inorganic and with organic dopants. Basically,an effective electron transfer occurs from the dopant to the matrixincreasing the Fermi level of the matrix. For an efficient transfer in ap-doping case, the LUMO energy level of the dopant is preferably morenegative than the HOMO energy level of the matrix or at least slightlymore positive, not more than 0.5 eV, to the HOMO energy level of thematrix. For the n-doping case, the HOMO energy level of the dopant ispreferably more positive than the LUMO energy level of the matrix or atleast slightly more negative, not lower than 0.5 eV, to the LUMO energylevel of the matrix. It is further more desired that the energy leveldifference for energy transfer from dopant to matrix is smaller than+0.3 eV.

Typical examples of known redox doped hole transport materials are:copperphthalocyanine (CuPc), which HOMO level is approximately −5.2 eV,doped with tetrafluoro-tetracyanoquinonedimethane (F4TCNQ), which LUMOlevel is about −5.2 eV; zincphthalocyanine (ZnPc) (HOMO=−5.2 eV) dopedwith F4TCNQ; a-NPD(N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine) doped withF4TCNQ. a-NPD doped with 2,2′-(perfluoronaphthalene-2,6-diylidene)dimalononitrile (PD1). a-NPD doped with2,2′,2″-(cyclopropane-1,2,3-triylidene)tris(2-(p-cyanotetrafluorophenyl)acetonitrile)(PD2). All p-doping in the device examples of the present applicationwas done with 8 wt. % of PD2.

Typical examples of known redox doped electron transport materials are:fullerene C60 doped with acridine orange base (AOB);perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) dopedwith leuco crystal violet; 2,9-di(phenanthren-9-yl)-4,7-diphenyl-1,10-phenanthroline doped with tetrakis(1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinato) ditungsten(II)(W₂(hpp)₄); naphthalene tetracarboxylic acid di-anhydride (NTCDA) dopedwith 3,6-bis-(dimethyl amino)-acridine; NTCDA doped withbis(ethylene-dithio) tetrathiafulvalene (BEDT-TTF).

It was found that phosphepine compounds comprising at least onephosphine oxide group may be successfully converted to highly conductiveelectron transport semiconducting materials by electrical doping withmetals. Such electrically doped semiconducting material can be easilyprepared by co-deposition of metal vapours with the vapour of aphosphepine compound comprising at least one phosphine oxide group on asolid substrate. Besides alkali metals, this method of electrical dopingworks very well also for other metals with significantly higherionization potentials and lower reductive power. Their lower reactivityis thus especially advantageous for easy handling in industrialmanufacturing processes. Particularly advantageous n-dopants forphosphepine electron transport matrices comprising at least onephosphine oxide group are alkaline earth metals and rare earth metals.Typical representatives of these groups are magnesium and ytterbium,which are particularly advantageous due their favourable vaporizationtemperatures under high vacuum conditions, which fit well withvaporization temperatures of typical electron transport matrixcompounds.

It was further found that classical redox dopants with high reductionstrenght, expressed as a highly negative redox potential measured bycyclic voltammetry (CV) in THF vs. Fc+/Fc standard, may be inphosphepine electron transport matrices successfully replaced with metalsalts having no pronounced reductive properties. True mechanism howthese compounds, sometimes called “electrically doping additives”,contribute to the lowering of the voltage in electronic devices, is notyet known.

Typical known representative of such metal salts is lithium8-hydroxyquinolinolate (LiQ) represented by the formula D1

Many other similar lithium complexes comprising five- or six-memberedchelate ring wherein Li is coordinated to an oxygen and a nitrogen atomare known and were used or proposed as electrical dopants for organicelectron transporting semiconducting materials.

As already stated above, the doped semiconducting material according toone of preferred embodiments comprises lithium salt having generalformula (II)

wherein A¹ is a C₆-C₃₀ arylene or C₂-C₃₀ heteroarylene comprising atleast one atom selected from O, S and N in an aromatic ring and each ofA²-A³ is independently selected from a C₆-C₃₀ aryl and C₂-C₃₀ heteroarylcomprising at least one atom selected from O, S and N in an aromaticring, wherein any aryl, arylene, heteroaryl and/or heteroarylene may beindependently unsubstituted or substituted with groups selected fromhydrocarbon groups comprising only C and H, alkoxy, aryloxy andlithiumoxy, provided that the given C count in an aryl, heteroaryl,arylene or heteroarylene group includes also all substituents present onthe said group.

It is to be understood that the term substituted or unsubstitutedarylene stands for a divalent radical derived from substituted orunsubstituted arene, wherein the both adjacent structural moieties (informula (II), the OLi group and the diaryl phosphine oxide group) areattached directly to an aromatic ring of the arylene group. Similarly,the term substituted or unsubstituted heteroarylene stands for adivalent radical derived from substituted or unsubstituted heteroarene,wherein the both adjacent structural moieties (in formula (II), the OLigroup and the diaryl prosphine oxide group) are attached directly to anaromatic ring of the heteroarylene group. Example compounds of thisclass of dopants are represented by structures D2 and D3

Compound D2 was disclosed in the application PCT/EP2012/074127,published as WO2013/079678 A1, and compound D3 in the applicationEP13170862.

The lithium complex (II) works in the inventive semiconducting materialas an electrical dopant, whereas the phosphepine compound has thefunction of a charge transporting matrix.

Phosphepine Matrix Compound

The phosphepine ring is a specific example of a conjugated system ofdelocalized electrons. The phosphepine compound used in the inventioncomprises at least one conjugated system with at least 6 delocalizedelectrons, preferably with at least 10 delocalized electrons, morepreferably with at least 14 delocalized electrons. In another preferredembodiment, the phosphepine compound comprises at least two conjugatedsystem of delocalized electrons linked with the phosphorus atom.

Examples of conjugated systems of delocalized electrons are systems ofalternating pi- and sigma bonds, wherein, optionally, one or moretwo-atom structural units having the pi-bond between its atoms can bereplaced by an atom bearing at least one lone electron pair, typicallyby a divalent O or S atom. Alternatively or in an addition, the systemof alternating pi- and sigma bonds may embed one or more isolated boronatoms having only six valence electrons and one vacant orbital.Preferably, the conjugated system of delocalized electrons comprises atleast one aromatic ring adhering to the Hückel rule. More preferably,the conjugated system of delocalized electrons comprises a condensedaromatic skeleton comprising at least 10 delocalized electrons, e.g. anaphthalene, anthracene, phenanthrene, pyrene, benzofurane orbenzothiophene skeleton. Also preferably, the conjugated system ofdelocalized electrons may consist of at least two directly attachedaromatic rings, the simplest examples of such systems being biphenyl,bithienyl, phenylthiophene, furylthiophene and like.

In one embodiment of the invention, the phosphepine ring comprises atleast one polycyclic aromatic or a polycyclic heteroaromatic system ofdelocalized electrons. The polycyclic (hetero)aromatic system may bedirectly attached to the phosphorus atom, or may be separated from thephosphorus atom by a double bond or by a monocyclic aromatic orheteroaromatic ring.

In one preferred embodiment of the invention, the lowest unoccupiedmolecular orbital (LUMO) of the phosphepine matrix compound is localizedmainly on a polycyclic aromatic or heteroaromatic ring system. As a ruleof thumb, it can be supposed that the presence of at least 10 fullydelocalized electrons in the conjugated (hetero)aromatic system makesthe lowest unoccupied molecular orbital of the whole phosphepine matrixcompound localized mainly on the polycyclic (hetero)aromatic ringsystem.

More specifically, the localization of a frontier orbital like LUMO inthe molecule can be assigned by a skilled person to that part of themolecule which contains the largest conjugated pi-electron system. Incase that two or more pi-electron systems with the same extent (given bythe number of pi electrons in conjugation) occur in the molecule, thelowest energy can be assigned to the system linked with strongestelectron withdrawing groups and/or weakest electron donating groups. Theelectron withdrawing and/or electron accepting effects of varioussubstituents are commensurate to experimentally accessible parameterslike Hammet or Taft constants which are tabulated for large number ofsubstituents most frequently occurring in aromatic or heteroaromaticorganic compounds. In most cases, the above mentioned parameters aresufficient for a reliable LUMO localization, because the overall effectof more substituents attached to the same aromatic system is additive.In case of uncertainty, the ultimate method for the correct LUMOlocalization in the molecule is quantum chemical calculation. Reliableresults with relatively low demand for computational capacity providefor example the methods based on density functional theory (DFTmethods).

It is desirable that the LUMO level of the phosphepine matrix compound,measured as a redox potential by cyclic voltammetry (CV) intetrahydrofuran (THF) against ferrocenium/ferrocene redox couple as areference, is in the range −1.8-−3.1 V. It is preferred that the energyof this LUMO is in the range −2.0-−2.9 V, more preferably in the range−2.15-2.75 V, even more preferably in the range −2.25-−2.6 V. Modernquantum chemical methods allow also a reliable estimation of relativeLUMO energies for different molecules. The computed relative values canbe recalculated to absolute scale corresponding to the electrochemicalpotentials measured in a concrete CV experimental setting, if thecalculated value is compared with the value measured for the samecompound and the obtained difference is taken into account as acorrection for the values calculated for other compounds.

An example of phosphepine matrix compound which has been proven as avery effective charge transport compound in organic electronic devicesis compound E1

The synthesis of new phophepine compounds according to invention wasaccomplished by synthesis procedures known in the art. First option isthe synthesis method described by W. Winter, Chem. Ber. 109, (1976), p.2405-2419 for 1,2,3,4,9-pentaphenyltribenzo[b,d,f]phosphepine 9-oxideaccording to formula A1

Using (1,1′-biphenyl-4-yl)phosphine dichloride instead ofphenylphosphine dichloride as the starting material in the samesynthesis protocol, the inventive compound B1 was obtained

Another option is the synthesis method described for compound E1 by M.and K. Mereiter, Bull. Chem. Soc. Jpn., 76, 1233-1244 (2003).

Using compound C5

in this synthesis protocol as the starting material instead C4, theauthors of the present application prepared compound E2

Still another option is a condensation of dimetallaterphenyl precursorswith arylphosphonous dichlorides, analogously to procedure described inScience of Synthesis 17 (2004), pages 916-917. The dimetallaterphenylprecursors are accessible by method described by Wittig et al, ChemischeBerichte (1962), 95, 431-42.

V. AVANTAGEOUS EFFECT OF THE INVENTION

The favourable effects of the electron-transporting matrix compounds inorganic semiconducting materials are shown in comparison withcomparative devices comprising instead of the phosphepine compoundelectron transporting matrices which lack the phosphepine group.Comparative compounds C1-C4 characterized in more detail in the examplesare referred to.

Table 1 shows the performance of compound E1 and comparative compoundsin bottom emission structured OLEDs, described in detail in example 1,with respect to voltage (U) and quantum efficiency (Qeff). Additionally,the values of the CIE 1931 coordinate y are given as a measure ofsimilar spectral distribution of luminance in the compared devices andvalues of the average time necessary for the 3% change in the initialluminance (LT97) at the room temperature are reported as anotherparameter for the compound performance. The LUMO energy level isexpressed in terms of redox potential estimated by cyclic voltammetry bystandard procedure using tetrahydrofuran as a solvent andferrocene/ferrocenium as reference redox couple.

TABLE 1 D1 doped D2 doped LUMO LT97 LT97 Code (V) U (V) Qeff Q/U CIEy(h) U (V) Qeff Q/U CIEy (h) E1 −2.62 4.9 5.4 1.10 375 4.9 6.5 1.33 0.095215 C1 −2.27 4.9 5.5 1.12 0.094 510 4.8 6.9 1.44 0.092 150 C2 −2.19 4.74.9 1.04 0.096 266 5.0 5.6 1.12 0.098 226 C3 −2.24 4.1 6.5 1.59 0.103 514.2 7.1 1.69 0.103 70 C4 −2.69 6.7 4.0 0.60 0.105 0.2 6.6 6.5 0.98 0.1001.8

Table 2 shows the performance of compounds E1 and E2 as electroninjection layer in a blue fluorescent OLED described in Example 3.Performance parameters are defined analogously as in Table 1.

TABLE 2 Yb doped D4 doped LUMO LT97 LT97 Code (V) U (V) Qeff Q/U CIEy(h) U (V) Qeff Q/U CIEy (h) E1 −2.62 3.5 5.8 1.66 0.098 na 3.4 5.4 1.590.098 na E2 −2.91 3.4 5.5 1.62 0.093 na 3.3 5.2 1.58 0.092 na

The results show that in comparison with phosphine oxide matrixcompounds lacking the phosphepine ring, electrically doped phosphepineP-oxides afford high performance semiconducting materials even at veryhigh LUMO levels of the matrix compound (expressed as very negativeredox potentials). Furthermore, in comparison with other phosphine oxidematrix compounds, the performance of electrically doped semiconductingmaterials which are based on phosphepine matrix compounds depends onlyweakly on the extent of the delocalized system of conjugated electronscomprised in the matrix compound. This feature affords new degrees offreedom for design of organic semiconducting materials and electronicdevices comprising such semiconducting materials.

I. EXAMPLES

General Remarks for Synthesis:

All reactions with moisture- and/or air-sensitive agents were carriedout under argon atmosphere using oven dried glassware. Startingmaterials were used as purchased without further purification.Materials, which were used to build OLEDs, were sublimed by gradientsublimation to achieve highest purity.

Auxiliary Procedures

Cyclic Voltammetry

The redox potentials given at particular compounds were measured in anargon-deaerated, dry 0.1M THF solution of the tested substance, underargon atmosphere, with 0.1M tetrabutylammonium hexafluorophosphatesupporting electrolyte, between platinum working electrodes and with anAg/AgCl pseudo-standard electrode, consisting of a silver wire coveredby silver chloride and immersed directly in the measured solution, withthe scan rate 100 mV/s. The first run was done in the broadest range ofthe potential set on the working electrodes, and the range was thenadjusted within subsequent runs appropriately. The final three runs weredone with the addition of ferrocene (in 0.1M concentration) as thestandard. The average of potentials corresponding to cathodic and anodicpeak of the studied compound, after subtraction of the average ofcathodic and anodic potentials observed for the standard Fc⁺/Fc redoxcouple, afforded finally the reported value.

Analytics:

Final materials were characterized by mass spectrometry (MS) and protonmagnetic resonance (¹H-NMR). NMR samples were dissolved in CD₂Cl₂ unlessotherwise stated. Melting points (mp) were determined by differentialscanning calorimetry (DSC). Peak temperatures are reported. If gaschromatography—mass spectrometry (GC-MS) or high performance liquidchromatography (HPLC) with electrospray ionization mass spectroscopy(ESI-MS) were used for the product characterization, only themass/charge (m/z) ratios for the molecular peak are reported. Forbrominated intermediates, the corresponding isotopic multiplet isreported.

11-Phenylbenzo[b]dinaphtho[2,1-d:1′,2′-f]phosphepine-11-oxide (E1)

Step 1

[1,1′-Binaphthalen]-2,2′-diylbis(diphenylphosphine oxide) (C4)

(1,1′-Binaphthalen-2,2′-diyl)bis(diphenylphosphine) (124.00 g, 199.14mmol, 1 eq) was suspended in dichloromethane (1.75 L) and cooled to 5°C. with an ice bath. Hydrogen peroxide (61.0 mL, 597.4 mmol, 3 eq) wasadded slowly to the suspension within 1 h. The ice bath was removed andthe suspension was stirred overnight at room temperature. The mixturewas washed in portions with brine (2×150 mL per 600 mL reactionsolution). The organic phase was collected, dried over sodium sulphate,filtered and the solvent was evaporated. The crude product was suspendedin a mixture of n-hexane and DCM (400 mL, 95:5, vol:vol), filtered,washed with n-hexane and dried under vacuum overnight.

Yield: 125.07 g (96%), white powder.

Purity: HPLC: 99.5%

-   -   Melting point: 302° C. (from DSC (peak at 10 K/min))

Step 2

11-Phenylbenzo[b]dinaphtho-[2,1-d:1′,2′-f]phosphepine-11-oxide) (E1)

[1,1′-Binaphthalene]-2,2′-diylbis(diphenylphosphine oxide, (C4)) (65.47g, 100.00 mmol, 1 eq) was suspended in dry THF (655 mL) under argonatmosphere. After cooling the suspension to 0° C. with an ice bath, theLDA-solution (100.00 mL, 200.00 mmol, 2 eq) was added dropwise within 40min. The suspension was stirred for another 30 min at 0° C., then theice bath was removed and stirring was continued for 2.5 h at roomtemperature. After quenching the reaction by the addition of HCl (13 mL,2 M), a white precipitate was formed. The suspension was stirred foradditional 30 min and then the precipitate was collected by filtration.The crude product was washed with n-hexane (3×100 mL) and water (2×100mL). Then the solid material was suspended in water (200 mL), sonicatedfor 15 min, and filtered. The solid material was washed with water untilthe filtrate was neutral (2×100 mL). To increase the purity, the solidmaterial was washed with THF (50+25 mL) and acetonitrile (3×50 mL). Theproduct was dried under vacuum at 40° C.

Yield: 37.15 g (82%), white powder.

Purity: HPLC: 99.9%

-   -   Melting point: 330° C. (from DSC (peak at 10 K/min))

9-Phenyltribenzo[b,d,f]phosphepine-9-oxide (E2)

diphenyl(pyren-1-yl)phosphine oxide (C1)

Known (CAS 110988-94-8) for long, e.g. from JP 4 876 333 B2,commercially available.

(9,10-di(naphthalen-2-yl)anthracen-2-yl)diphenylphosphine oxide (C2)

Synthesis according to EP 2 860 782 A1

phenyldi(pyren-1-yl)phosphine oxide (C3)

Known for long (CAS 721969-93-3), commercially available, e.g. fromLuminescence Technology Corp (TW).

[1,1′-binaphthalene]-2,2′-diylbis(diphenylphosphine oxide) (C4)

The well-known compound (CAS 86632-33-9) is easily obtainable as anintermediate in the E1 synthesis described above.

1,2,3,4,9-pentaphenyltribenzo[b,d,f]phosphepine 9-oxide (A1) and

9-([1,1′-biphenyl]-4-yl)-1,2,3,4-tetraphenyltribenzo[b,d,f]phosphepine9-oxide (B1)

Both compounds were prepared according to procedure described by W.Winter, Chem. Ber. 109, (1976), p. 2405-2419.

ESI-MS (A1): 657 (M+H), 679 (M+Na); (B1): 731 (M+H), 753 (M+Na)

Dopants:

lithium quinolin-8-olate (D1)

Commercially available

lithium 2-(diphenylphosphoryl)phenolate (D2)

Synthesis according to patent application WO2013/079678 (compound (1),p. 15-16)

lithium 2-(diphenylphosphoryl)pyridin-3-olate (D3)

Prepared according to patent application EP 2 811 000.

lithium tetra-(1H-pyrazol-1-yl)borate (D4)

Prepared according to patent application WO2013/079676 (compound (7), p.16-17)

DEVICE EXAMPLES

Auxiliary materials used in device examples not explained above

N3,N3′-di([1,1′-biphenyl]-4-yl)-N3,N3′-dimesityl-[1,1′-biphenyl]-3,3′-diamine,described in WO2014/060526, F1;

biphenyl-4-yl(9,9-diphenyl-9H-fluoren-2-yl)-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-amine,CAS 1242056-42-3, F2;

1-(4-(10-(([1,1′-biphenyl]-4-yl)anthracen-9-yl)phenyl)-2-ethyl-1H-benzo[d]imidazole,CAS 1254961-38-0, F3.

All data shown here are typical examples. The data in table 1 aremedians over typically 16 identical diodes, which are described in thefollowing examples.

EXAMPLE 1

Bottom emission blue emitting OLED was made by depositing a 10 nm layerof HTM1 doped with PD2 (matrix to dopant weight ratio of 92:8 wt. %)onto a 90 nm thick ITO-glass substrate (ITO serves as an anode),followed by an 120 nm undoped layer of HTM1. Subsequently, a bluefluorescent emitting layer of ABH113 (Sun Fine Chemicals) doped withNUBD370 (Sun Fine Chemicals) (97:3 wt %) was deposited with a thicknessof 20 nm. A 36 nm layer of the tested inventive or comparative compoundwas deposited on the emitting layer together with 50 wt. % D1 or D2 asETL. Subsequently a layer of aluminium with a thickness of 100 nm wasdeposited as a cathode.

The observed voltages and quantum efficiencies at the current density 10mA/cm² are reported in the Table 1.

FIG. 3 and FIG. 4 depict OLED performance curves of devices comprisingas electron transporting matrices compounds E1 or C1-C4, respectively.The phosphepine matrix compound E1 performs equally well as thestate-of-the-art matrices C1-C2, and markedly better than its closestacyclic analogue C4 lacking the phosphepine ring. Compound C3 that gaveexperimental devices with slightly better operational voltage andefficiency as E1, in parallel shortened three times the device lifetime.As shows the Table 1, even much more dramatic difference in the lifetimewas observed in devices wherein E1 was replaced with its closest acyclicanalogue C4, because this comparative compound caused very quick changeof initial luminance and voltage in the operating devices.

All the data underline the unexpected beneficial effect of introducing aphosphepine unit into known triaryl phosphine oxide electron transportmaterials.

EXAMPLE 2 Use as a Matrix for Metal-Doped Pn-Junction in a Tandem WhiteOLED

On an ITO substrate, following layers were deposited by vacuum thermalevaporation: 10 nm thick HTL consisting of 92 wt. % auxiliary materialF2 doped with 8 wt. % PD2, 135 nm thick layer of neat F2, 25 nm thickblue emitting layer ABH113 (Sun Fine Chemicals) doped with NUBD370 (SunFine Chemicals) (97:3 wt. %), 20 nm thick layer ABH036 (Sun FineChemicals), 10 nm thick CGL consisting of 95 wt. % compound E1 dopedwith 5 wt. % Yb, 10 nm thick HTL consisting of 90 wt. % auxiliarymaterial F2 doped with 10 wt. % PD2, 30 nm thick layer of neat F2, 15 nmthick layer of neat F1, 30 nm thick proprietary phosphorescent yellowemitting layer, 35 nm thick ETL of auxiliary material F3, 1 nm thick LiFlayer and aluminium cathode. The diode operated at 6.71 V had EQE 23.7%.

EXAMPLE 3 Use as a Matrix in an EIL Doped with Metal or Metal Salt

Bottom emission blue emitting OLED was made analogously as in Example 1,except that the ETL was an undoped 34 nm thick layer made of neat ABH113and between the ETL and the aluminium cathode was deposited a 4 nm thickEIL consisting of matrix compound E1 or E2 doped with 50 wt. % Yb or D4.

The observed voltages and quantum efficiencies at the current density 10mA/cm² are reported in the Table 2.

The features disclosed in the foregoing description, in the claims andin the accompanying drawings may both separately and in any combinationbe material for realizing the invention in diverse forms thereof.

Used Acronyms and Abbreviations

CV cyclic voltammetry

CGL charge generating layer

DCM dichloromethane

DSC differential scanning calorimetry

DFT density functional theory

DME 1,2-dimethoxyethane

EE ethylester (ethyl acetate)

ETL electron transporting layer

EQE external quantum efficiency of electroluminescence

Fc⁺/Fc ferrocenium/ferrocene reference system

HPLC high performance liquid chromatography

HOMO highest occupied molecular orbital

HTL hole transporting layer

LUMO lowest unoccupied molecular orbital

LDA lithium diisopropyl amide

NMR nuclear magnetic resonance

SPS solvent purification system

TGA thermogravimetry thermal analysis

THF tetrahydrofuran

TLC thin layer chromatography

UV UV/Vis spectroscopy

eq chemical equivalent

mol. % molar percent

wt. % weight (mass) percent

mp melting point

n.a. not applicable

OLED organic light emitting diode

ITO indium tin oxide

The invention claimed is:
 1. Compound comprising at least onephosphepine ring and having the phosphorus atom of the phosphepine ringsubstituted with at least one monovalent substituent R, wherein R isselected from aryls or heteroaryls comprising at least two rings. 2.Compound according to claim 1, comprising at least one phosphine oxidegroup.
 3. Compound according to claim 1, wherein the phosphepine ring isa phosphepine-P-oxide ring.
 4. Compound according to claim 1, whereinthe substituent R is selected from C₁₀-C₆₆ aryl or C₄-C₆₆ heteroaryl. 5.Compound according to claim 1, having a structure according to formula(Ia):

wherein R¹ is selected from aryls or heteroaryls comprising at least tworings, and R²-R³ is a chain of six carbon atoms comprising sixpi-electrons, optionally substituted with hydrocarbon groups comprisingoverall up to 60 carbon atoms or with substituents consisting of overallup to 100 covalently bound atoms.
 6. Semiconducting material comprisinga compound according to claim
 1. 7. Semiconducting material according toclaim 6 further comprising at least one dopant.
 8. Semiconductingmaterial according to claim 7, wherein the dopant is an electricaldopant.
 9. Semiconducting material according to claim 8, wherein theelectrical dopant is an n-dopant.
 10. Semiconducting material accordingto claim 9, wherein the n-dopant is selected from a metal, a metal saltor a metal complex.
 11. Electronic device comprising the semiconductingmaterial according to claim
 6. 12. Electronic device according to claim11, wherein the semiconducting material forms at least one layer betweenan anode and a cathode.
 13. Electronic device according to claim 12,wherein the layer comprising the semiconducting material is an electrontransporting layer, an electron injecting layer, or fulfils bothelectron transporting and hole blocking function.
 14. Electronic deviceaccording to claim 11, which is a light emitting device.
 15. Electronicdevice according to claim 14, which is an organic light emitting diode.16. Compound according to claim 5, wherein the covalently bound atomsare selected from C, H, B, Si, N, O, S, P, F, Cl, Br, or I.